Expand stairs plot-type entry intro

Author: CouldNot

galleries/plot_types/basic/stairs.py

@@ -3,7 +3,8 @@
 stairs(values)
 ==============
 
-See `~matplotlib.axes.Axes.stairs`.
+See `~matplotlib.axes.Axes.stairs` when plotting $y$ between $(x_i, x_{i+1})$.
+For plotting $y$ at $x$, see `~matplotlib.axes.Axes.step`.
 
 .. redirect-from:: /plot_types/basic/step
 """